exhaust smell

[UFO]

Just another thought.
Is the exhaust manifolds/headers been coated recently?

[poppa]

No , but thanks.

[b5blue]

I noticed a nasty smell running my car (Six pack also.) after adding octane boost. Unknown to me at the time I had a gummed up center bowl and weak spark from sitting too much. How's the car running? The smell cleared up after burning that tank load up. (I fixed the issues it had while still burning up that fuel.)
I'd check all the grounds for the body and engine, go over the ignition connections and check that the center carb has a good squirt from the accelerator pump as that was the give away that the bowl was getting gummy. If all is well run that load of fuel down and get fresh fuel.